Glossary
Definitions
10 definitions
G/T (Figure of Merit)
The ratio of receive antenna gain (G) to system noise temperature (T), expressed in dB/K — the fundamental measure of a receiver's sensitivity in a satellite link. A higher G/T means a receiver can detect weaker signals, enabling smaller transmitting antennas or longer link distances.
GEO (Geostationary Orbit)
Fixed orbit at 35,786 km above the equator where satellites appear stationary relative to Earth, enabling permanent coverage of one-third of the globe with a single satellite, but with 550+ ms round-trip latency.
GNSS / GPS
Global Navigation Satellite Systems (GNSS) are constellations of MEO satellites — GPS (USA), Galileo (EU), GLONASS (Russia), BeiDou (China) — that broadcast precise timing signals enabling receivers on Earth to calculate their position with metre or sub-metre accuracy.
GPS Spoofing
A cyberattack that transmits counterfeit GPS signals stronger than genuine satellite signals to deceive a receiver into computing a false position — used to mislead ship navigation, redirect drones, or manipulate timing-dependent systems, with incidents documented in the Black Sea, Persian Gulf, and near conflict zones.
Galileo (GNSS System)
The European Union's global satellite navigation system — 30 satellites at 23,222 km MEO — operated by the EU Agency for the Space Programme (EUSPA), providing civilian open service at 1–5 m accuracy and a High Accuracy Service at better than 20 cm, fully interoperable with GPS and other GNSS.
Gateway
A large ground station that aggregates satellite capacity from one or more spot beams and connects it to the terrestrial internet or private network backbone, acting as the interface between the space and ground segments.
Globalstar
A US mobile satellite operator running 24 LEO satellites at 1,414 km altitude in L-band (user) and S-band (satellite-to-user) for voice, messaging, and IoT services — known for Apple's Emergency SOS satellite feature on iPhone 14+ (2022), which uses dedicated Globalstar frequencies.
Green Propulsion
Spacecraft propulsion technologies that replace highly toxic hydrazine monopropellant with less hazardous alternatives — including ammonium dinitramide (ADN)-based propellants (LMP-103S, AF-M315E), electric propulsion (xenon/krypton ion thrusters), and cold gas thrusters using non-toxic gases — improving safety and reducing handling costs.
Ground Segment
All Earth-based infrastructure that supports a satellite system — including gateway stations, TT&C facilities, network operations centres, and mission control — responsible for controlling the satellite, processing data, and connecting the space segment to terrestrial networks.
Ground Station
Earth-based facility equipped with antennas and signal processing equipment for two-way communication with satellites: transmitting commands and receiving telemetry, data, or user traffic.